Analog Top Talks in May on EDABoard.com forums

Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around analog ICs and analog design. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com.

Signal generator instability – I have built this signal generator and I have noticed that is quite stable on the KHz region but as it passes to the MHz frequency starts to get more and more drift. I was wondering what could be the source of this drift which appears only in the MHz region? I have used molded chokes with ferrite cores, which could possibly be the case, but is that really only that, or is it the design of the circuit that causes the drift itself? Read more

Fractional frequency divider using sigma-delta modulator –  am working on sigma-delta modulator that I need to use in the fractional divider. I know why the noise shaping occurs in sigma-delta and can see it in the simulation of 2 and order sigma-delta (Verilog model). I am applying 1 kHz sine wave at modulator input and using sampling clock of 1Meg. The noise shaping is present around the frequency of 1kHz, at modulator output however when I use this modulator to control the divider (changing the dividing factor) I can’t see the noise shaping around the output signal of divider. Read more

Noise in CMOS inverter – 1) Why would CMOS inverter perform poorly in terms of supply noise rejection ratio? Could anyone explain maths equations?
2) Could anyone elaborate on this statement “The output resistance is a good measure of the sensitivity of the gate in respect to noise-induced at the output, and is preferably as low as possible”?
3) Could anyone suggest a good circuit methodology to measure the output resistance of CMOS inverter? Read more

Pulsar circuit for ultrasonic transducer – I am working on Pulsar circuit which will drive ultrasonic transducer. I need to exit transducer at 600v to 800v, but pulsar circuit provides 400v max. even if VDD is 600v. Read more

IR2110S driver failed when suddenly – I’m facing one issue with IR2110S driver while driving 3 winding BLDC moto r(24V,8A rating with Hall sensor feedback) using IFR3710 MOSFET (Half-bridge configuration). When varying duty cycle from 0 to 100 present with 5 percent interval, the motor running fine. But when varying duty cycle (PWM) from 0 to 70 percent suddenly, IR2110S driver IC getting failed (with more than 60 percent duty cycle interval observing this effect). Read more

Using allpass filter as 90-degree phase shift – I am trying to use an allpass filter as 90-degree phase shifter.
Using UPC815c as op amp with Rx = 5.1Ω , C =12pF and calculating R = 1/(2ΠfC) = 978Ω, where Power frequency f = 13.56MHz. My problem is that amplitude of the output fluctuates too much and phase shift reading from input to output also fluctuates from negative to positive while testing on an oscilloscope (like -130, -85 , -30,-5, 16,48,60,92,94,114,144..etc). Read more

Preamp design in flash ADC – Considering that a pre-amplifier compares the input voltage with a special voltage obtained from a resistive ladder in a Flash ADC. I would like to know whether the design of pre-amplifiers is different from each other? Read more

Crystal oscillator and load capacitor – Why is there a 3x larger capacitor on the right side of the crystal? Read mor

Stability analysis and weird behaviour – When plotting the closed loop stability analysis, what happens if the gain crosses the 0dB more than once? Say, three times? The same for the phase margin plot. What happens of it “crosses” the 0dB more than once? Read more

Are 50-ohm transmission lines required for 2.4GHz amplifier? – I am designing a 2.4 GHz pre-amp. Is it required to have 50-ohm transmission lines (microstrip I’m guessing) at the nodes of the circuit? Or will regular copper work? Should I put components back to back with each other, or put 50-ohm transmission line in between? Or could I just use a regular multipurposePCBb board and solder the components together? Read more